President Donald Trump's tweets Sunday morning claiming he denied Sen. Bob Corker's request for an endorsement are false, two sources familiar with the discussions said.

Trump told Corker he was going to endorse him the day the Tennessee Republican announced his intention to retire, the sources said.

"The President called the senator early last week and asked him to reconsider his decision not to seek re-election and reaffirmed that he would have endorsed him, as he has said many times," one of the sources said.

Trump attacked Corker in a series of tweets Sunday, days after the Tennessee Republican made public comments criticizing him, prompting Corker to respond by tweeting an insult later in the morning calling the White House "an adult day care center."

The flare-up between the two leaders highlights the long-simmering differences between GOP leaders and the President, who has not shied away from attacking the leadership over their inability to move health care legislation. It also comes as Trump prepares to press Congress to advance his proposed tax overhaul and tensions reportedly grow between Trump and members of his own Cabinet -- especially Secretary of State Rex Tillerson -- on issues such as the way to handle North Korea's nuclear weapons program.

Corker's vote will be critical on tax reform, and he remains an influential voice on Trump's foreign policy challenges, including over how to handle the Iran nuclear deal.

It's not the first time Trump and the White House have privately sent one signal to Corker while publicly saying something else. Following Corker's pointed attack on Trump for his handling of the deadly violence in Charlottesville, Virginia, in August, Vice President Mike Pence quietly sought to repair ties with Corker after the President attacked the Tennessee Republican on Twitter, sources said.

Corker responded shortly after: "It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning," Corker wrote.